An arc flash can release a deadly blast of energy without any warning, making it one of the more frightening hazards involved with electrical work. Dropping a tool, opening a panel on degraded equipment, and even pest infestations can trigger an arc flash; it’s very difficult to predict and prevent them. However, there’s one factor that unites all arc flash incidents, and can be controlled: all arc flashes require electrical power.
As a result of this simple fact, the accepted industry standard for safe electrical work (NFPA 70E) recommends a simple approach to completely eliminate the risk of arc flash when working on electrical equipment: shut it off and lock it out.
An employee works within the Limited Approach Boundary, a clearance area around equipment designed to prevent unqualified workers form being exposed to a hazard of electric shock
A worker faces an increased risk of injury from arc flash, as a result of the nature of their work or the equipment being worked on
In both of these cases, the most effective way to protect the worker is to keep the equipment in a de-energized state, with no electrical power. Where there is no power, there is no risk or electric shock or arc flash!
De-energizing the equipment is only part of the electrically safe work condition, though. Imagine you’re working on equipment that’s been powered down for safety; all of the electrical hazards have been essentially eliminated. Then, another worker enters the room and flips a switch to start working on their own tasks. That could be catastrophic, unless you can be certain that the equipment you’re working on can’t be accidentally started up again. That certainty is the idea behind lockout/tagout (LO/TO).
Shut down the equipment and disconnect those power sources
Apply locks and tags to keep the power sources disconnected
Confirm that the equipment is completely de-energized
With electrical work, the same basic ideas still apply, but some additional steps may be called for. All affected workers should be informed that equipment will be disconnected temporarily, and should be told why this is the case, so there is no misunderstanding. Many electrical systems can carry power without any obvious indication that they’re still energized, so the NFPA requires using appropriate testing tools to confirm the absence of power. If procedures aren’t tailored for the actual hazards and situations that are present in a facility, accidents and injuries are going to remain a problem.
The NFPA 70E standard includes an example of an effective LO/TO procedure in Informative Annex G. As experts in safety, the NFPA makes recommendations to double-check each critical point in the process. The following steps are based on the NFPA’s description in that informative annex.
Notify all affected employees that equipment is being shut down, and provide the reasons for doing so.
Identify all sources of electrical power to the equipment.
Shut down the equipment and disconnect any energy sources.
Relieve any stored energy appropriately (by grounding, attempting to start the equipment, or other means).
Apply locks and tags to all disconnecting devices.
Verify that locks are properly applied.
Use an appropriate testing tool to verify that the equipment is de-energized, and then verify that the tool is functioning correctly by testing a known voltage source.
Where necessary, install a grounding device to eliminate the risk of induced or stored voltage.
After this process is complete, the equipment will be in an electrically safe work condition, and work may continue.
OSHA’s Rules for LO/TO and Arc Flash Safety
While the NFPA standard represents expert advice and industry consensus, it’s not strictly required by law. Instead, workplace safety in the United States falls under the jurisdiction of OSHA and their regulations. OSHA’s general requirements for safe electrical work practices are in 29 CFR 1910.333, and a basic approach for working on de-energized equipment, including a LO/TO system, appears in paragraph (b) of those rules. These rules generally align with OSHA’s more extensive LO/TO rules in 29 CFR 1910.147, which go into more detail about the lockout or tagout devices that should be used.
Because these regulations can only be changed or updated through a long and involved process at the federal agency, it’s common for facilities that prioritize safety to look to experts like the NFPA for advice on protecting their workers. In fact, where a given question is not covered by regulations, OSHA frequently uses NFPA standards like NFPA 70E as an example of common industrial safety practices. Practices that do not follow common guidelines for safety may indicate disregard for safety.
A system that meets all of the NFPA’s recommendations for safe practices will typically satisfy OSHA’s requirements; because the NFPA updates most of their standards every three years, staying up-to-date with their recommendations will also show that a facility is paying attention to new developments in safe work practices.
Preventing Arc Flash in Your Facility
Where electrical hazards exist in your facility, it’s important to train the affected workers to understand those hazards and follow safe practices. Employees who aren’t performing work on a given piece of powerful equipment should know about the equipment’s “danger zones” and how far back to stay. Finally, when work must be performed on energized equipment, your qualified workers need to have the resources to stay safe. That includes detailed equipment labels to keep them informed of details such as what personal protective equipment (PPE) they need to wear.
If you are ready to build a LO/TO system for your workplace, or if you want to learn more about how to apply this kind of system for safety, request a free guide to Lockout/Tagout Best Practices.